1. Field of the Invention
The present invention relates to a silicon wafer etching process, more particularity, to a photoelectrochemical etching process of silicon wafer which uses ammonium fluoride and halogen light illumination in the photoelectrochemical etching process.
2. Description of the Prior Art
Presently, wafer etching technology includes a dry-etching process and a wet-etching process.
Those etching processes have many advantages and disadvantages as follows:
Dry-etchingWet-etching processprocessChemical EtchingElectrochemical EtchingCostExpensiveCheap, but causesVery cheappollutionProductionLowHighHighAspect>20:1>20:1>20:1RatioTrenchbelow 0.5 μmbelow 0.5 μmbelow 0.5 μmAppear-Excellent, butNormalExcellentance ofhaving manyetchingwaves in holeholewallSubstrateEtchingEtching directionEtching directiondirectionpertinent to thepertinent to theimpertinent tocrystallizationcrystallization direction,the substratedirection ofsemiconductor categorysubstrateand resistance ofsubstrate
Using the dry-etching process results in the best hole structure. Because the equipment is expensive and is hard to maintain, the production cost is higher. On the other hand, the wet-etching process could add to the production cost because the resultant pollution of crystallization surface and potassium ions.
The wet etching process was developed in 1958, Turner (Journal of the Electrochemical Society, vol. 105, pp. 402, 1958) disclosed a porous silicon layer on the surface of a silicon wafer using hydrofluoric acid solution in an electropolishing process. From 1958 to 1990, the development of the electropolishing process concentrated on decreasing the thickness of the silicon wafer, publishing process, and discussion on generating and application of a porous layer on an n-type silicon wafer. In 1990, Lehmann (Journal of the Electrocheminal Society, Vol. 137, pp. 653, 1990) first disclosed the macropore array with high density and high aspect ratio on the silicon wafer by the electropolishing process.
The conventional wet-etching used hydrofluoric acid as the etching solution. The hydrofluoric acid has odorless and unpalatable properties and easily forms fluoride, the boiling point is 19.54° C., is volatile and damages people at room temperature, the disadvantages are as follows:    1. The nose, throat, eyes and respiratory organs will be seriously damage by being exposed to air containing 122 ppm hydrofluoric acid for one minute.    2. People are killed by being exposed to air containing 50 ppm hydrofluoric acid for a couple of minutes (refer to the reference).    3. People are killed by being superficiously splashed with hydrofluoric acid.    4. Hydrofluoric acid easily reacts with the calcium of the human body to generate fluoride, which fluoride can lead to toxication, bone softening, changing sex and bone hardening.    5. Fluorine toxication leads diseases of the heart, nervous system and gut.
Further, the appearance of the hole is not smooth and equable by using hydrofluoric acid as an etching solution in the wet-etching process, so the results are unacceptable.